High impedance antenna



Sept. 26, 1950 Filed May 14, 1947 RAYMOND F. 'SMELTZER Patented Sept.26, 1950 HIGH IMPEDANCE ANTENNA Raymond F. Smeltzer, Towson, Md,assignor to Bendix Aviation Corporation, Towson, Md., a

corporation of Delaware Application May 14, 1947, Serial No. 748,023

This invention is directed to antennas, and more specifically it isdirected to antennas hav-- ing a comparatively high radiationresistance.

The problem of providing a good impedance match between a conventionalsymmetrical half wave antenna, having a self-impedance, or radia- I tionresistance, of the order of '72 ohms, and a parallel wire transmissionline of reasonable dimensions, and having a characteristic impedance ofthe order of several hundred ohms, has

3 Claims. (01. 250-33) been the subject of study by communicationsworkers for many years. One of the most promising solutions to thisproblem is the folded dipole or T-match antenna which provides an inputor driving-point impedance roughly equal to four times the radiationresistance of the simple dipole. .The folded dipole, however, suffersthe shortcoming that it is necessarily a cumbersome mechanicalarrangement, and also has the limita tion that its radiation resistancecan not be varied over a wide range without using a structure ofconductors having differing diameters.

A further shortcoming of prior art antennas oi-t-he symmetrical dipoleclass is that they are generally suitable for use over only acomparatively narrow band of frequencies in the vicinity of the optimumdesign frequency.

It is an object of this invention to provide an antenna having acomparatively high radiation resistance. g

It is a further object of this invention 'to provide an antenna capableof being used with substantially constant efficiency over acomparatively wide band of frequencies.

It is a further object of this inventionto provide an antenna, theradiation resistance of which may be continuously varied over a widerange by alteration of the lengths of its component conductors.

These objects are accomplished by the use of a pair of parallelradiating elements outwardly extending from a region of overlap betweentheir proximate 1 portions.

The above and further objects and advantages of this invention will morefully appear from the following detailed description when the same isread in conjunction with the accompanying drawing wherein there isillustrated schematically an antenna constituting one embodiment of theinstant invention.

Referring now to the drawing there is illustrated a pair of parallelconductors Ill having outwardly extending portions h, and parallelproximate portions Z. The portions 1 are separated by a distanceindicated s. A transmission line I! comprising a pair of spacedpara1lelcon ductors is connected to the conductors It] at the points ofdemarcation between the portions h andl. v.

' In o'peration, the dimension'h is chosen to be slightly greater'thanone quarter wavelength at the mean operating frequency of the system,

and the length of the overlap Z and the magnitude of thespacing s. is'chosen to have a reactance equal and opposite to the reactance presentedby the extended portions. For example, if it is desired to match a 500ohm transmission line to the antenna, a dimension It can be found whichpresents a radiation resistance of 500 ohms. This resistance will beaccompanied by an inductive reactance which may be cancelled by properchoice of the length Z and the spacing s.

Mathematical expressions for the calculation of the exact dimensions ofthe antenna to provide the relationships set forth above are availablein standard text books such as Transmission Lines,

Antennas and Waveguides, by King, Mimno and Wing, published in 1945 byMcGraw-Hill Book Company, Inc., New York city.

A typical antenna for covering the band between 88 and 106 megacycles,and matching a 300 ohm transmission line has been found to have thefollowing dimensions I h=3i A inches 8:1 inch,

1:4 inches While it is recognized that antennas having an overlapportion at their center are known to the art, it must be pointed outthat in their design there was no concept of dimensioning them to attainthe relationships outlined herein, and that the overlap in the prior artantennas is strictly for mechanical reasons.

What is claimed is:

1. An antenna comprising a pair of radiating elements each slightlygreater than an electrical quarter wave in length; a stub matchingsection less than an electrical quarter wave in length interposedbetween and joined to the said radiating elements; and a transmissionline connected to the points of junction between the said elements andthe said matching section the said radiating elements being of suchlength as to prevent a partially reactive impedance to the saidtransmission line, and the said matching section being of such length asto present a reactance equal in magnitude and opposite in sign to thereactive component of the said impedance.

2. An antenna comprising a pair of radiating elements each slightlygreater than an electrical quarter wave in length; a stub matchingsection less than an electrical quarter wave in length interposedbetween and joined to the said radiating elements; and a transmissionline connected to the points of junction between the said elements andthe said matching section the said stub being a linear extension of theradiating elements.

3. An antenna comprising a pair of radiating elements each slightlygreater than an electrical quarter wave in length; a stub matchingsection ance.

RAYMOND F. SMELTZER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,280,738 Bace Apr. 21, 19422,299,218 Fener Oct. 20, 1942 2,311,364 Buschlech Feb. 16, 1943 '252,417,895 Wheeler Mar. 25, 1947 Certificate of Correction Patent No.2,523,728 September 26, 1950 RAYMOND F. SMELTZER It is hereby certifiedthat error appears in the printed specification of the above numberedpatent requiring correction as follows:

Column 3, line 8, for the word prevent read present;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOffioe.

Signed and sealed this 5th day of December, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

